During the course of electroplating metals, the metals undergoing plating are typically subjected to rinsing operations, for example, to remove residual plating chemicals from the surface of the metals. As a consequence of such rinsing operations, considerable volumes of rinse water solutions are generated and these are commonly contaminated with hazardous chemicals. Since the release of such materials to the environment is normally prohibited by law, the waste water streams must be treated prior to their release.
In the case of copper plating processes, for instance, the water used to rinse the metal being plated quickly acquires environmentally unacceptable levels of hazardous substances, including heavy metals such as copper and chromium. These are often disposed of by precipitating the metals as water insoluble metal hydroxides which are subsequently removed primarily by flocculation and clarification through one of several types of gravity separators. However, clarification is basically a "rough in" process which requires final polishing to remove very small metal precipitate fines.
One method of removing the remaining solids has involved the use of a so-called "moving web filter" comprising the gravity filtration of the filtrate derived from a primary separation process through a paper filter media disposed on a supporting, liquid-permeable belt located in the bottom of a filter box or tray. During the secondary filtration process, the contaminated liquid is pumped into the tray where it diffuses across the filter media. Separation of the solids begins immediately by gravity flow through the media and its supporting belt to a filtrate tank positioned below the tray. Solids collect on the media until its pores become plugged, the level of the contaminated liquid then rising until a float control is activated. In response to a signal from the control, the motor-driven belt then stretches fresh media across the bottom of the tray, while the filtered solids are dragged over an incline which drains liquid off before collecting the separated solids and spent media in a "sludge box" provided for the purpose. A filter system of the type described, for example, is that manufactured by Serfilco Ltd. of Glenview, Ill., identified by that company as "an automatic fabric filtration system".
While the apparatus described performs the filtering operation in a satisfactory manner, it has the disadvantage of producing a large amounts of contaminated filter media, thus creating a disposal problem since the media is itself classified as a hazardous waste material due to the accumulation of the filtered solids in its pores.